Looks like an amaranth (red root pig weed) which has had its center stalk removed and has grown lateral branches. Quick way to id the plant is to pull it out roots and all. It will have a central tap root with branching side roots. The portion of the root just below the surface will be red in color with the rest of the root being white. The seed heads displayed in your photo will have small spikes that are sharp when handled with bare hands. Reference link: http://oregonstate.edu/dept/nursery-weeds/weedspeciespage/REDROOT/habit_3_750.jpg
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